1. Field of the Invention
This invention relates to a viewing surgical scope apparatus capable of introducing a visualization scope and a working device such as an energy delivery device in minimally invasive surgical procedures. In particular, the preferred procedure is transmyocardial revascularization "TMR" wherein the energy delivery device is an optical fiber element.
2. Discussion of Related Art
The human heart is a muscular dual pump that beats continuously throughout life sending blood to the lungs and the rest of the body. The interior of the heart consists of four distinct chambers. The septum, a thick central muscular wall, divides the cavity into right and left halves. On the right side, the upper half is known as the right atrium. Deoxygenated blood from the rest of the body arrives in the right atrium via the vena cava, the blood is pumped across a one-way valve known as the tricuspid valve into the lower portion known as the right ventricle. From there the blood circulates to the lungs through the pulmonary valve via the pulmonary artery where it is oxygenated by circulation through the alveoli of the lungs (not shown). The blood returns via the pulmonary veins to the left atrium and flows through a second valve, the mitral valve into the left ventricle where it is pumped via the aorta to the rest of the body.
Much of the heart consists of a special type of muscle called myocardium. The myocardium requires a constant supply of oxygen and nutrients to allow it to contract and pump blood throughout the vasculature. The inner surfaces of the chambers of the heart are lined with a smooth membrane, the endocardium, and the entire heart is enclosed in a tough, membranous bag known as the pericardial sac.
The pumping action of the heart has three main phases for each heart beat. Diastole is the resting phase during which the heart fills with blood: while deoxygenated blood is entering the right atrium, oxygenated blood is returned from the lungs to the left atrium. During atrial systole, the two atria contract simultaneously, squeezing the blood into the lower ventricles. Finally, during ventricular systole the ventricles contract to pump the deoxygenated blood into the pulmonary arteries and the oxygenated blood into the main aorta. When the heart is empty, diastole begins again. The electrical impulses which stimulate the heart to contract in this manner emanate from the heart's own pacemaker, the sinoatrial node. The heart rate is under the external control of the body's autonomic nervous system.
Though the heart supplies blood to all other parts of the body, the heart itself has relatively little communication with the oxygenated blood supply. Thus, the two coronary arteries, the left coronary artery and the right coronary artery, arise from the aorta and encircle the heart muscle on either side "like a crown" to supply the heart itself with blood.
Heart disorders are a common cause of death in developed countries. They also impair the quality of life of millions of people and restrict activity by causing pain, breathlessness, fatigue, fainting spells and anxiety. The major cause of heart disease in developed countries is impaired blood supply. The coronary arteries become narrowed due to atherosclerosis and part of the heart muscle is deprive of oxygen and other nutrients. The resulting ischemia or blockage can lead to angina pectoris; a pain in the chest, arms or jaw due to lack of oxygen to the heart's myocardium, or infarction; or tissue necrosis in myocardial tissue.
Techniques to supplement the flow of oxygenated blood directly from the left ventricle into the myocardial tissue have included needle acupuncture to create transmural channels (see below) and implantation of T-shaped tubes into the myocardium. Efforts to graft the omentum, parietal pericardium, or mediastinal fat to the surface of the heart had limited success. Others attempted to restore arterial flow by implanting the left internal mammary artery into the myocardium.
Modernly, coronary artery blockage can be relieved in a number of ways. Drug therapy, including nitrates, beta-blockers, and peripheral vasodilator drugs (to dilate the arteries) or thrombolytic drugs (to dissolve clots) can be very effective. If drug treatment fails transluminal angioplasty is often indicated--the narrowed part of the artery, clogged with atherosclerotic plaque or other deposits, can be stretched apart by passing a balloon to the site and gently inflating it a certain degree. In the event drug therapy is ineffective or angioplasty is too risky (often introduction of a balloon in an occluded artery can cause portions of the atherosclerotic material to become dislodged which may cause a total blockage at a point downstream of the subject occlusion, thereby requiring emergency procedures, the procedure known as coronary artery bypass grafting (CABG) is the most common and successful major heart operation performed, with over 500,000 procedures done annually in America alone. The procedure takes at least two surgeons and can last up to five hours. First, the surgeon makes an incision down the center of the patient's chest and the heart is exposed by opening the pericardium. A length of vein is removed from another part of the body. The patient is subjected to cardiopulmonary bypass during the operation. The section of vein is first sewn to the aorta and then sewn onto a coronary artery at a place such that oxygenated blood can flow directly into the heart. The patient is then closed. Not only does the procedure require the installation of the heart-lung machine, a very risky procedure, but the sternum must be sawed through and the risk of infection is enhanced during the time the chest cavity is spread open.
Another method of improving myocardial blood supply is called transmyocardial revascularization (TMR), the creation of channels from the epicardial to the endocardial portions of the heart. The procedure uses needles to perform "myocardial acupuncture," that has been experimented with at least as early as the 1930s and used clinically since the 1960s, see Deckelbaum. L. I., Cardiovascular Applications of Laser Technology, Lasers in Surgery and Medicine 15:315-341 (1994). This technique has relieved ischemia by allowing blood to pass from the ventricle through the channels either directly into other vessels perforated by the channels or into myocardial sinusoids which connect to the myocardial microcirculation. This procedure has been likened to transforming the human heart into one resembling that of a reptile. In the reptile heart, perfusion occurs via communicating channels between the left ventricle and the coronary arteries. Frazier, O. H., Myocardial Revascularization with Laser--Preliminary Findings, Circulation, 1995; 92 [suppl II:II-58-II-65]. There is evidence of these communicating channels in the developing human embryo. In the human heart, myocardial microanatomy involves the presence of myocardial sinusoids. These sinusoidal communications vary in size and structure, but represent a network of direct arterial-luminal, arterial-arterial, arterial-venous, and venous-luminal connections. This vascular mesh forms an important source of myocardial blood supply in reptiles but its role in humans is not well understood.
Numerous TMR studies have been performed using lasers where channels are formed in the myocardium. In one study, 20-30 channels per square centimeter were formed into the left ventricular myocardium of dogs prior to occlusion of the arteries. LAD ligation was conducted on both the revascularized animals as well as a set of control animals. Results showed that animals having undergone TMR prior to LAD ligation acutely showed no evidence of ischemia or infarction in contrast to the control animals. After sacrifice of the animals post operatively between 4 weeks and 5 months, the laser-created channels could be demonstrated grossly and microscopically to be open and free of debris and scarring.
It is possible that the creation of laser channels in the myocardium may promote long-term changes that could augment myocardial blood flow such as by inducing angiogenesis in the region of the lazed (and thus damaged) myocardium. Support for this possibility is reported in histological evidence of probable new vessel formation adjacent to collagen occluded transmyocardial channels. In the case of myocardial acupuncture or boring, which mechanically displaces or removes tissue, acute thrombosis followed by organization and fibrosis of clots is the principal mechanism of channel closure. By contrast, histological evidence of patent, endothelium-lined tracts within the laser-created channels supports the assumption that the inside of the laser channels is or can become hemocompatible and that it resists occlusion caused by thrombo-activation and/or fibrosis.
U.S. patents that deal with TMR and myocardial revascularization include U.S. Pat. No. 4,658,817 which teaches a method and apparatus for TMR using a laser. A surgical CO.sub.2 laser includes a handpiece for directing a laser beam to a desired location. Mounted on the forward end of the handpiece is a hollow needle to be used in surgical applications where the needle perforated a portion of tissue to provide the laser beam direct access to distal tissue. U.S. Pat. No. 5,125,926 teaches a heart-synchronized pulsed laser system for surgical TMR. This patent's system and method include a sensing device for synchronized firing of a laser during the contraction and expansion of a beating heart during a predetermined portion of the heartbeat cycle. This heart-synchronized pulsed laser system is important where the type of laser, the energy and pulse rate are potentially damaging to the beating heart or its action. Additionally, as the heart beats, the spatial relationship between the heart and the tip of the laser delivery probe may change so that the necessary power of the beam and the required position of the handpiece may be unpredictable. U.S. Pat. No. 5,380,316 teaches of TMR performed by inserting a portion of an elongated flexible lasing apparatus into the chest cavity of a patient and lasing channels directly through the outer surface of the epicardium into the myocardium tissue. U.S. Pat. Nos. 5,389,096 and 5,607,421 teach of myocardial revascularization that is performed by guiding an elongated flexible lasing apparatus into a patient's vasculature percutaneously such that the firing end of their respective lasing apparatus are adjacent the endocardium for lasing channels directly through the endocardium into myocardium tissue without perforating the heart's pericardium layer. None of the above listed patents teach methods for performing myocardial revascularization using minimally invasive surgical techniques, nor do their respective system's include a device for visualizing areas of the heart during such a procedure.
Patent literature that deals with minimally invasive surgical procedures for myocardial revascularization includes PCT application WO 97/13468 and U.S. Pat. No. 5,700,259 which teach of thoracoscopic myocardial revascularization devices using a CO.sub.2 type laser based handpiece. U.S. Pat. No. 5,685,857 teaches of a thoracoscopic cannula device. PCT application WO 97/34540 teaches of video assisted thoracoscopic CO.sub.2 type laser TMR surgical method for a thoracoscopic myocardial revascularization procedure.
Finally, viewing devices used in cardiac interventional procedures include U.S. Pat. Nos. 4,784,133 and 4,976,710 which both teach of an angioscope/bronchoscope device that includes a flexible distal end with an inflatable balloon structure for viewing intravasculature structures. This device's flexible catheter includes a working channel for introducing a procedural device at the viewing/treatment distal end.
There is a need for an apparatus and method for performing myocardial revascularization from one or more minimally invasively formed penetrations and eliminating the need for open chest surgery by providing a viewing surgical scope allowing for single handed use during such a procedure.